Class UnionSubclassPersister

A BasicEntityPersiter maps an entity to a single table in a relational
database.

A persister is always responsible for a single entity type.

EntityPersisters are used during a UnitOfWork to apply any changes to the
persistent state of entities onto a relational database when the UnitOfWork is
committed, as well as for basic querying of entities and their associations (not
DQL).